Chip resistors are structured so that a resistive element made, for instance, of ruthenium oxide is positioned between a pair of electrode sections. However, a chip resistor used, for instance, for electronic circuit current detection needs to have a resistance value of not higher than 1Ω. A technology that uses a resistive element made mainly of copper to obtain such a low-resistance chip resistor has long been known (refer, for instance, to Patent Document 1).
FIG. 5 is a cross-sectional schematic view illustrating a conventionally known low-resistance chip resistor. The chip resistor 1 shown in FIG. 5 includes a resistive element 3, which is made mainly of a copper-nickel alloy and positioned on the upper surface of a ceramic substrate 2, which is shaped like a rectangular parallelepiped. A pair of upper electrodes 4 is positioned in a region covering both longitudinal ends of the resistive element 3. The resistive element 3 exposed between the pair of upper electrodes 4 is covered with an insulating protective layer 5 that is made, for instance, of glass. Further, end-face electrodes 6 are positioned on both longitudinal end faces of the ceramic substrate 2. The upper ends of the end-face electrodes 6 overlap with the upper electrodes 4 and are closely joined. In addition, each end-face electrode 6 is covered, for instance, with two plating layers (nickel-plating layer 7 and solder-plating layer 8) to avoid electrode loss and provide enhanced solder reliability. In some cases, a tin-plating layer may be formed in place of the solder-plating layer.
When the chip resistor 1 configured as described above is to be mounted on a circuit board 30, the pair of end-face electrodes 6, which are extended over both longitudinal ends of the lower surface of the ceramic substrate 2, are placed on the associated solder land 31a of a wiring pattern 31 of the circuit board 30 and subjected to a solder connection process so that the plating layers 7, 8 covering the end-face electrodes 6 are connected with solder 32 to the solder land 31a to establish an electrical and mechanical connection. The copper-nickel alloy has a small temperature coefficient of resistance (TCR). Therefore, when the resistive element 3 is made mainly of a copper-nickel alloy, it is possible to obtain a low-resistance, low-TCR chip resistor having a resistance value setting of not higher than 1Ω. Patent Document 1: Japanese Patent Application Laid-Open Publication No. H10-144501 (pages 4 and 5, FIG. 1)